Motor vehicles are very commonly equipped with hydraulic brake systems, and these are almost universally fitted to modern automobiles and light trucks. Such systems have a master cylinder which is connected to a brake pedal which is depressed by the foot of the vehicle operator; as this is done, hydraulic fluid is forced from the master cylinder (which also includes a reservoir for supplying fluid to the system) through brake lines to the several wheel cylinders, causing their actuation.
After maintenance has been performed on a hydraulic brake system of this type, it is typically necessary to remove any air which may have been introduced into the system as a result of the various fittings and components having been disturbed. If this air is not removed, the bubbles in the brake lines and elsewhere will tend to compress when the system is actuated, causing "sponginess" and a loss of braking effectiveness. The process of removing the air from the brake system is commonly referred to as "bleeding". Typically, bleed screws are mounted at each of the wheel cylinders (as well as elsewhere in some systems) for permitting the air to escape at these points as hydraulic fluid is forced into the system from the master cylinder. Normally, the bleeding process requires two people. The first person goes to a selected wheel cylinder and operates the bleed screw, while the second person sits in the car and pumps the brake pedal; the first person observes the brake fluid and air bubbles flowing from the bleed screw, and opens and closes this, and shouts instructions to the second person to operate the brake pedal as necessary.
This conventional approach to brake bleeding is obviously fraught with serious deficiencies. Firstly, it requires the services of a two personnel, thus requiring excessive expenditure of valuable time and labor. Furthermore, the shouted instructions may not always be correctly interpreted by the person operating the brake pedal, or precisely responded to, so that the effort may be poorly coordinated. Also, the traditional technique requires one of the mechanics to sit in the car, which presents the potential for damage to the interior from oil and grease on the mechanics' clothing, or from tools inadvertently left in a pocket. Still further, many modern brake systems require an application of a very even amount of pressure to the brake pedal during each part of the bleeding operation, and such very even pressure is simply very difficult for a human operator to apply manually.
Attempts have been made to overcome some of these deficiencies. One approach has taken the form of what are known to those skilled in the art as "power bleeders". These are typically cannister-like containers which are partially filled with brake fluid and then pressurized with air. The brake fluid is fed under pressure through a flexible conduit to a fitting which is sealingly mounted to the reservoir on the master cylinder. The fluid pressure from the pressure bleeder is communicated through the master cylinder and brake lines to the wheel cylinders, so as to force fluid through the brake lines and evacuate the air. Such power bleeders are not completely satisfactory. Among the practical disadvantages which they exhibit is the fact that they are invariably messy to use, and spilled brake fluid can cause serious damage to a vehicle's paint finish. Furthermore, a number of specialized parts are required; due to the many configurations of master cylinders, there is no one "universal" type of fitting which will sealingly mount to all of these, and so even a reasonably well-equipped mechanic may find himself without suitable fittings for anything but the most ubiquitous systems. The need for all these specialized fittings also contributes to increased costs. Perhaps even more importantly, ordinary power bleeders can supply only a steady fluid pressure to the brake system, and cannot provide any sort of "pumping" action; this is becoming a more and more serious deficiency in view of the fact that this "pumping" action is required for the proper bleeding of the many modern anti-lock braking systems which are coming into use in both automobiles and light trucks.
Accordingly, there exists a need for a device which selectively pumps the brake pedal of a vehicle while the brake system is being bled by an operator who is located adjacent one of the wheel cylinders, remote from the brake pedal. Furthermore, there exists a need for such a device which is substantially universal in nature so that it can be detachably installed in at least the great majority of vehicles without requiring specialized attachment fittings. Also, a need exists for such a device which is able to deliver an equal and even amount of pressure to the brake pedal as each part of the system is bled. Still further, there is a need for such a device which is economical to fabricate and reliable to operate.